Universität zu Köln

Motte, F., Luong, Q. Nguyen, Schneider, N., Heitsch, F., Glover, S., Carlhoff, P., Hill, T., Bontemps, S., Schilke, P., Louvet, F., Hennemann, M., Didelon, P. and Beuther, H. (2014). The formation of the W43 complex: constraining its atomic-to-molecular transition and searching for colliding clouds. Astron. Astrophys., 571. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. Numerical simulations have explored the possibility of forming molecular clouds through either a quasi-static, self-gravitating mechanism or the collision of gas streams or lower density clouds. They also quantitatively predict the distribution of matter at the transition from atomic to molecular gases. Aims. We aim to observationally test these models by studying the environment of W43, a molecular cloud complex recently identified near the tip of the Galactic long bar. Methods. Using Galaxy-wide HI and (CO)-C-12 1-0 surveys, we searched for gas flowing toward the W43 molecular cloud complex. We also estimated the HI and H-2 mass surface densities to constrain the transition from atomic to molecular gas around and within W43. Results. We found three cloud ensembles within the position-velocity diagrams of (CO)-C-12 and HI gases. They are separated by similar to 20 km s(-1) along the line of sight and extend into the (CO)-C-13 velocity structure of W43. Since their velocity gradients are consistent with free fall, they could be nearby clouds attracted by and streaming toward the W43 similar to 10(7) M-circle dot potential well. We show that the HI surface density, Sigma(HI) = 45-85 M-circle dot pc(-2), does not reach any threshold level but increases when entering the 130 pc-wide molecular complex previously defined. This suggests that an equilibrium between H-2 formation and photodissociation has not yet been reached. The H-2-to-HI ratio measured over the W43 region and its surroundings, R-H2 similar to 3.5 +/-(3)(2), is high, indicating that most of the gas is already in molecular form in W43 and in structures several hundred parsecs downstream along the Scutum-Centaurus arm. Conclusions. The W43 molecular cloud complex may have formed and, in fact may still be accreting mass from the agglomeration of clouds. Already in the molecular-dominated regime, most of these clouds are streaming from the Scutum-Centaurus arm. This clearly disagrees with quasi-static and steady-state models of molecular cloud formation.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Motte, F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Luong, Q. Nguyen UNSPECIFIED UNSPECIFIED UNSPECIFIED Schneider, N. UNSPECIFIED UNSPECIFIED UNSPECIFIED Heitsch, F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Glover, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Carlhoff, P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Hill, T. UNSPECIFIED UNSPECIFIED UNSPECIFIED Bontemps, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Schilke, P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Louvet, F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Hennemann, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Didelon, P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Beuther, H. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-423810
DOI:	10.1051/0004-6361/201323001
Journal or Publication Title:	Astron. Astrophys.
Volume:	571
Date:	2014
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language GALACTIC RING SURVEY; WARM NEUTRAL HALOS; STAR-FORMATION; MILKY-WAY; H-I; RED SUPERGIANTS; GRAVITATIONAL COLLAPSE; INTERSTELLAR-MEDIUM; RAPID FORMATION; MINI-STARBURST Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/42381